dr. wolf's chm 201 & 202 18-1 chapter 18 carboxylic acids
TRANSCRIPT
Dr. Wolf's CHM 201 & 202 18-1
Chapter 18Chapter 18Carboxylic AcidsCarboxylic Acids
Dr. Wolf's CHM 201 & 202 18-2
Carboxylic Acid NomenclatureCarboxylic Acid Nomenclature
Dr. Wolf's CHM 201 & 202 18-3
Table 18.1 Table 18.1 Table 18.1 Table 18.1
Systematic NameSystematic NameOO
HCOHHCOH methanoic acidmethanoic acid
OO
CHCH33COHCOH ethanoic acidethanoic acidOO
CHCH33(CH(CH22))1616COHCOH octadecanoic acidoctadecanoic acid
systematic IUPAC names replace "-e" systematic IUPAC names replace "-e" ending of alkane with "oic acid"ending of alkane with "oic acid"
Dr. Wolf's CHM 201 & 202 18-4
Table 18.1Table 18.1Table 18.1Table 18.1
Systematic NameSystematic Name Common NameCommon NameOO
HCOHHCOH methanoic acidmethanoic acid formic acidformic acid
OO
CHCH33COHCOH ethanoic acidethanoic acid acetic acidacetic acidOO
CHCH33(CH(CH22))1616COHCOH octadecanoic acidoctadecanoic acid stearic acidstearic acid
common names are based on natural origin common names are based on natural origin rather than structurerather than structure
Dr. Wolf's CHM 201 & 202 18-5
Table 18.1Table 18.1Table 18.1Table 18.1
Systematic NameSystematic Name Common NameCommon Name
2-hydroxypropanoic2-hydroxypropanoicacidacid
lactic acidlactic acid
((ZZ)-9-octadecenoic)-9-octadecenoicacidacid
oleic acidoleic acid
OO
CHCH33CHCOHCHCOH
OHOH OO
(CH(CH22))77COHCOH
CC CC
HH HH
CHCH33(CH(CH22))77
Dr. Wolf's CHM 201 & 202 18-6
Structure and BondingStructure and Bonding
Dr. Wolf's CHM 201 & 202 18-7
Formic acid is planarFormic acid is planarFormic acid is planarFormic acid is planar
Dr. Wolf's CHM 201 & 202 18-8
Formic acid is planarFormic acid is planarFormic acid is planarFormic acid is planar
CC OO
HH
HH
OO
120 pm120 pm
134 pm134 pm
Dr. Wolf's CHM 201 & 202 18-9
Electron DelocalizationElectron DelocalizationElectron DelocalizationElectron Delocalization
RRCC
OOHH
OO••••
•••• ••••
•••• RRCC
OOHH
OO••••
•••• ••••
••••++••••
––
Dr. Wolf's CHM 201 & 202 18-10
Electron DelocalizationElectron DelocalizationElectron DelocalizationElectron Delocalization
stabilizes carbonyl groupstabilizes carbonyl group
RRCC
OOHH
OO••••
•••• ••••
•••• RRCC
OOHH
OO••••
•••• ••••
••••++••••
–– RRCC
OOHH
OO••••
••••
••••
++
••••
––
Dr. Wolf's CHM 201 & 202 18-11
Physical PropertiesPhysical Properties
Dr. Wolf's CHM 201 & 202 18-12
Boiling PointsBoiling PointsBoiling PointsBoiling Points
Intermolecular forces, especially hydrogen Intermolecular forces, especially hydrogen bonding, are stronger in carboxylic acids than bonding, are stronger in carboxylic acids than in other compounds of similar shape and in other compounds of similar shape and molecular weightmolecular weight
bpbp 31°C31°C 80°C80°C 99°C99°C
OHOH
141°C141°C
OHOH
OO OO
Dr. Wolf's CHM 201 & 202 18-13
Hydrogen-bonded DimersHydrogen-bonded DimersHydrogen-bonded DimersHydrogen-bonded Dimers
Acetic acid exists as a hydrogen-bonded Acetic acid exists as a hydrogen-bonded dimer in the gas phase. The hydroxyl group dimer in the gas phase. The hydroxyl group of each molecule is hydrogen-bonded to the of each molecule is hydrogen-bonded to the carbonyl oxygen of the other.carbonyl oxygen of the other.
HH33CCCC
OO HH OO
CCHCCH33
OOHHOO
Dr. Wolf's CHM 201 & 202 18-14
Hydrogen-bonded DimersHydrogen-bonded DimersHydrogen-bonded DimersHydrogen-bonded Dimers
Acetic acid exists as a hydrogen-bonded Acetic acid exists as a hydrogen-bonded dimer in the gas phase. The hydroxyl group dimer in the gas phase. The hydroxyl group of each molecule is hydrogen-bonded to the of each molecule is hydrogen-bonded to the carbonyl oxygen of the other.carbonyl oxygen of the other.
Dr. Wolf's CHM 201 & 202 18-15
carboxylic acids are similar to alcohols in respect carboxylic acids are similar to alcohols in respect to their solubility in waterto their solubility in water
form hydrogen bonds to waterform hydrogen bonds to water
Solubility in WaterSolubility in WaterSolubility in WaterSolubility in Water
HH33CCCC
OO HH OO
OOHHOO
HH
HH
HH
Dr. Wolf's CHM 201 & 202 18-16
Acidity of Carboxylic AcidsAcidity of Carboxylic Acids
Most carboxylic acids have a pMost carboxylic acids have a pKKaa close to 5. close to 5.
Dr. Wolf's CHM 201 & 202 18-17
but carboxylic acids are far more acidic than alcoholsbut carboxylic acids are far more acidic than alcohols
Carboxylic acids are weak acidsCarboxylic acids are weak acidsCarboxylic acids are weak acidsCarboxylic acids are weak acids
CHCH33COCOHH
OO
CHCH33CHCH22OOHH
KKaa = 1.8 x 10 = 1.8 x 10-5-5
ppKKaa = 4.7 = 4.7KKaa = 10 = 10-16-16
ppKKaa = 16 = 16
Dr. Wolf's CHM 201 & 202 18-18
GG°= 91 kJ/mol°= 91 kJ/mol
GG°= 27 kJ/mol°= 27 kJ/mol
GG°= 64 kJ/mol°= 64 kJ/mol
Free Energies of IonizationFree Energies of IonizationFree Energies of IonizationFree Energies of Ionization
CHCH33CHCH22OO– – + H+ H++
CHCH33CHCH22OHOH CHCH33COCOHH
OO
CHCH33COCO–– + H + H++
OO
Dr. Wolf's CHM 201 & 202 18-19
Greater acidity of carboxylic acids is attributedGreater acidity of carboxylic acids is attributedstabilization of carboxylate ion bystabilization of carboxylate ion by
Greater acidity of carboxylic acids is attributedGreater acidity of carboxylic acids is attributedstabilization of carboxylate ion bystabilization of carboxylate ion by
inductive effect of carbonyl groupinductive effect of carbonyl group
resonance stabilization of carboxylate ionresonance stabilization of carboxylate ion
RCRC
OO
OO++
––
RCRC
OO
OO
––••••
••••
••••
••••
•••• ••••
••••
RCRC
OO
OO––
••••
••••••••
Dr. Wolf's CHM 201 & 202 18-20
Figure 19.4: Electrostatic potential maps ofFigure 19.4: Electrostatic potential maps ofacetic acid and acetate ionacetic acid and acetate ion
Figure 19.4: Electrostatic potential maps ofFigure 19.4: Electrostatic potential maps ofacetic acid and acetate ionacetic acid and acetate ion
Acetic acidAcetic acid Acetate ionAcetate ion
Dr. Wolf's CHM 201 & 202 18-21
Substituents and Acid Strength
Dr. Wolf's CHM 201 & 202 18-22
standard of comparison is acetic acid (standard of comparison is acetic acid (XX = H) = H)
Substituent Effects on AciditySubstituent Effects on Acidity
XX CHCH22COHCOH
OO
KKaa = 1.8 x 10 = 1.8 x 10-5-5
ppKKaa = 4.7 = 4.7
Dr. Wolf's CHM 201 & 202 18-23
Substituent Effects on AciditySubstituent Effects on Acidity
alkyl substituents have negligible effectalkyl substituents have negligible effect
XX CHCH22COHCOH
OO
XX KKaa ppKKaa
HH
CHCH33
CHCH33(CH(CH22))55
1.8 x 101.8 x 10-5-5 4.74.7
1.3 x 101.3 x 10-5-5 4.94.9
1.3 x 101.3 x 10-5-5 4.94.9
Dr. Wolf's CHM 201 & 202 18-24
Substituent Effects on AciditySubstituent Effects on Acidity
electronegative substituents increase acidityelectronegative substituents increase acidity
XX CHCH22COHCOH
OO
XX KKaa ppKKaa
HH
FF
ClCl
1.8 x 101.8 x 10-5-5 4.74.7
2.5 x 102.5 x 10-3-3 2.62.6
1.4 x 101.4 x 10-3-3 2.92.9
Dr. Wolf's CHM 201 & 202 18-25
Substituent Effects on AciditySubstituent Effects on Acidity
electronegative substituents withdraw electronegative substituents withdraw electrons from carboxyl group; increase electrons from carboxyl group; increase KK for for loss of Hloss of H++
XX CHCH22COHCOH
OO
Dr. Wolf's CHM 201 & 202 18-26
Substituent Effects on AciditySubstituent Effects on Acidity
effect of substituent decreases as number of bonds effect of substituent decreases as number of bonds between between XX and carboxyl group increases and carboxyl group increases
XX CHCH22COHCOH
OO
XX KKaa ppKKaa
HH 1.8 x 101.8 x 10-5-5 4.74.7
1.4 x 101.4 x 10-3-3 2.92.9
1.0 x 101.0 x 10-4-4 4.04.0ClCHClCH22
ClCl
3.0 x 103.0 x 10-5-5 4.54.5ClCHClCH22CHCH22
Dr. Wolf's CHM 201 & 202 18-27
Ionization ofSubstituted Benzoic Acids
Dr. Wolf's CHM 201 & 202 18-28
Hybridization EffectHybridization Effect
KKaa ppKKaa
6.3 x 106.3 x 10-5-5 4.24.2
5.5 x 105.5 x 10-5-5 4.34.3
1.4 x 101.4 x 10-2-2 1.81.8
COHCOH
OO
HH22CC CHCH COHCOH
OO
COHCOH
OO
HCHC CC
spsp22-hybridized carbon is more electron--hybridized carbon is more electron-withdrawing than withdrawing than spsp33, and , and spsp is more electron- is more electron-withdrawing than withdrawing than spsp22
Dr. Wolf's CHM 201 & 202 18-29
ppKKaa
SubstituentSubstituent orthoortho metameta paraparaHH 4.24.2 4.24.2 4.24.2CHCH33 3.93.9 4.34.3 4.44.4
FF 3.33.3 3.93.9 4.14.1ClCl 2.92.9 3.83.8 4.04.0CHCH33OO 4.14.1 4.14.1 4.54.5NONO22 2.22.2 3.53.5 3.43.4
Ionization of Substituted Benzoic AcidsIonization of Substituted Benzoic Acids COHCOH
OOXX effect is small unless X is effect is small unless X is
electronegative; effect is electronegative; effect is largest for ortho substituentlargest for ortho substituent
Dr. Wolf's CHM 201 & 202 18-30
Salts of Carboxylic Acids
Dr. Wolf's CHM 201 & 202 18-31
Carboxylic acids are neutralized by strong basesCarboxylic acids are neutralized by strong basesCarboxylic acids are neutralized by strong basesCarboxylic acids are neutralized by strong bases
equilibrium lies far to the right; equilibrium lies far to the right; KK is ~ 10 is ~ 101111
as long as the molecular weight of the acid is as long as the molecular weight of the acid is not too high, sodium and potassium not too high, sodium and potassium carboxylate salts are soluble in watercarboxylate salts are soluble in water
strongerstrongeracidacid
weakerweakeracidacid
RCOHRCOH ++ HOHO–– RCORCO–– ++ HH22OO
OOOO
Dr. Wolf's CHM 201 & 202 18-32
unbranched carboxylic acids with 12-18 carbonsunbranched carboxylic acids with 12-18 carbonsgive carboxylate salts that form give carboxylate salts that form micellesmicelles in inwaterwater
MicellesMicellesMicellesMicelles OO
ONaONasodium stearatesodium stearate
(sodium octadecanoate)(sodium octadecanoate)
CHCH33(CH(CH22))1616COCO
OO
NaNa++––
Dr. Wolf's CHM 201 & 202 18-33
MicellesMicellesMicellesMicelles OO
ONaONa
polarpolarnonpolarnonpolar
sodium stearate has a polar end (the carboxylate sodium stearate has a polar end (the carboxylate end) and a nonpolar "tail"end) and a nonpolar "tail"
the polar end is "water-loving" or hydrophilicthe polar end is "water-loving" or hydrophilic
the nonpolar tail is "water-hating" or hydrophobicthe nonpolar tail is "water-hating" or hydrophobic
in water, many stearate ions cluster together to form in water, many stearate ions cluster together to form spherical aggregates; carboxylate ions on the spherical aggregates; carboxylate ions on the outside and nonpolar tails on the insideoutside and nonpolar tails on the inside
Dr. Wolf's CHM 201 & 202 18-34
MicellesMicelles OO
ONaONa
polarpolarnonpolarnonpolar
Dr. Wolf's CHM 201 & 202 18-35
Figure 19.5 A micelleFigure 19.5 A micelleFigure 19.5 A micelleFigure 19.5 A micelle
Dr. Wolf's CHM 201 & 202 18-36
MicellesMicellesMicellesMicelles
The interior of the micelle is nonpolar and The interior of the micelle is nonpolar and has the capacity to dissolve nonpolar has the capacity to dissolve nonpolar substances.substances.
Soaps clean because they form micelles, Soaps clean because they form micelles, which are dispersed in water.which are dispersed in water.
Grease (not ordinarily soluble in water) Grease (not ordinarily soluble in water) dissolves in the interior of the micelle and is dissolves in the interior of the micelle and is washed away with the dispersed micelle.washed away with the dispersed micelle.
Dr. Wolf's CHM 201 & 202 18-37
Dicarboxylic Acids
Dr. Wolf's CHM 201 & 202 18-38
Dicarboxylic AcidsDicarboxylic Acids
one carboxyl group acts as an electron-one carboxyl group acts as an electron-withdrawing group toward the other; effect withdrawing group toward the other; effect decreases with increasing separationdecreases with increasing separation
Oxalic acidOxalic acid
Malonic acidMalonic acid
Heptanedioic acidHeptanedioic acid
1.21.2
2.82.8
4.34.3
COHCOH
OO
HOCHOC
OO ppKKaa
HOCCHHOCCH22COHCOH
OOOO
HOC(CHHOC(CH22))55COHCOH
OO OO
Dr. Wolf's CHM 201 & 202 18-39
Carbonic Acid
Dr. Wolf's CHM 201 & 202 18-40
Carbonic AcidCarbonic Acid
HOCOHHOCOH
OO
COCO22 ++ HH22OO
99.7%99.7% 0.3%0.3%
Dr. Wolf's CHM 201 & 202 18-41
Carbonic AcidCarbonic Acid
HOCOHHOCOH
OO
COCO22 ++ HH22OO HOCOHOCO––
OO
HH++ ++
Dr. Wolf's CHM 201 & 202 18-42
Carbonic AcidCarbonic Acid
HOCOHHOCOH
OO
COCO22 ++ HH22OO HOCOHOCO––
OO
HH++ ++
overall overall KK for these two steps = 4.3 x 10 for these two steps = 4.3 x 10-7-7
COCO22 is major species present in a solution of is major species present in a solution of
"carbonic acid" in acidic media"carbonic acid" in acidic media
Dr. Wolf's CHM 201 & 202 18-43
Carbonic AcidCarbonic Acid
HOCOHOCO––
OO
––OCOOCO––
OO
HH++ ++
KKaa = 5.6 x 10 = 5.6 x 10-11-11Second ionization constant:Second ionization constant:
Dr. Wolf's CHM 201 & 202 18-44
Sources of Carboxylic Acids
Dr. Wolf's CHM 201 & 202 18-45
side-chain oxidation of alkylbenzenes (Chapter 11) side-chain oxidation of alkylbenzenes (Chapter 11)
oxidation of primary alcohols (Chapter 15)oxidation of primary alcohols (Chapter 15)
oxidation of aldehydes (Chapter 17)oxidation of aldehydes (Chapter 17)
Synthesis of Carboxylic Acids: Review
Synthesis of Carboxylic Acids: Review
Dr. Wolf's CHM 201 & 202 18-46
Synthesis of Carboxylic Acids by the Carboxylation of
Grignard Reagents
Dr. Wolf's CHM 201 & 202 18-47
Carboxylation of Grignard ReagentsCarboxylation of
Grignard Reagents
RXRXMgMg
diethyldiethyletherether
RMgXRMgXCCOO22
HH33OO++
RRCCOMgXOMgX
OO
RRCCOHOH
OOconverts an alkyl (or converts an alkyl (or aryl) halide to a aryl) halide to a carboxylic acid having carboxylic acid having one more carbon atom one more carbon atom than the starting halidethan the starting halide
Dr. Wolf's CHM 201 & 202 18-48
RR
MgXMgX
CC
OO
••••
•••• MgXMgX++
––
HH33OO++
diethyldiethyletherether
OO ••••••••
––
RR CC
OO••••
•••• ••••
OO ••••••••
RR CC
OHOH••••
••••
OO ••••••••
Carboxylation of Grignard ReagentsCarboxylation of
Grignard Reagents
Dr. Wolf's CHM 201 & 202 18-49
Example: Alkyl HalideExample: Alkyl Halide
CHCH33CHCHCHCH22CHCH33
(76-86%)(76-86%)
1. Mg,1. Mg, diethyl ether diethyl ether
2. 2. CCOO22
3. H3. H33OO++
CHCH33CHCHCHCH22CHCH33
ClCl CCOO22HH
Dr. Wolf's CHM 201 & 202 18-50
Example: Aryl HalideExample: Aryl Halide
(82%)(82%)
1. Mg,1. Mg, diethyl diethyl ether ether
2. 2. CCOO22
3. H3. H33OO++
CHCH33
CCOO22HHBrBr
CHCH33
Dr. Wolf's CHM 201 & 202 18-51
Synthesis of Carboxylic Acidsby the
Preparation and Hydrolysis of Nitriles
Dr. Wolf's CHM 201 & 202 18-52
Preparation and Hydrolysis of Nitriles
Preparation and Hydrolysis of Nitriles
RXRX RRCCOHOH
OO
converts an alkyl halide to a carboxylic acid having converts an alkyl halide to a carboxylic acid having one more carbon atom than the starting halideone more carbon atom than the starting halide
limitation is that the halide must be reactive toward limitation is that the halide must be reactive toward substitution by Ssubstitution by SNN2 mechanism, i.e. best with primary, 2 mechanism, i.e. best with primary, then secondary…… tertiary gives eliminationthen secondary…… tertiary gives elimination
–– ••••••••CC NNRRCC ••••NN
SSNN22
HH33OO++
heatheat + NH+ NH44++
Dr. Wolf's CHM 201 & 202 18-53
ExampleExample
NaNaCCNN
DMSODMSO
(77%)(77%)
HH22OO
HH22SOSO44
heatheat
(92%)(92%)
CHCH22ClCl
CHCH22CCNN
CHCH22CCOHOH
OO
Dr. Wolf's CHM 201 & 202 18-54
Example: Dicarboxylic AcidExample: Dicarboxylic Acid
BrBrCHCH22CHCH22CHCH22BrBr
NaNaCCNN HH22OO
HH22O, HClO, HCl heatheat
(77-86%)(77-86%)NNCCCHCH22CHCH22CHCH22CCNN
(83-85%)(83-85%)HOHOCCCHCH22CHCH22CHCH22CCOHOH
OOOO
Dr. Wolf's CHM 201 & 202 18-55
via Cyanohydrinvia Cyanohydrin
1. Na1. NaCCNN
2. H2. H++
(60% from 2-pentanone)(60% from 2-pentanone)
HH22OO
HCl, heatHCl, heat
CHCH33CCHCCH22CHCH22CHCH33
OO
CHCH33CCHCCH22CHCH22CHCH33
OHOH
CCNN
CHCH33CCHCCH22CHCH22CHCH33
OHOH
CCOO22HH
Dr. Wolf's CHM 201 & 202 18-56
Reactions of Carboxylic Acids:A Review and a Preview
Dr. Wolf's CHM 201 & 202 18-57
Reactions of Carboxylic AcidsReactions of Carboxylic AcidsReactions of Carboxylic AcidsReactions of Carboxylic Acids
Acidity (Chapter 18)Acidity (Chapter 18)
Reduction with LiAlHReduction with LiAlH4 4 (Chapter 15)(Chapter 15)
Esterification (Chapter 15)Esterification (Chapter 15)
Reaction with Thionyl Chloride (Chapter 12)Reaction with Thionyl Chloride (Chapter 12)
Reactions already discussedReactions already discussed
Dr. Wolf's CHM 201 & 202 18-58
Reactions of Carboxylic AcidsReactions of Carboxylic AcidsReactions of Carboxylic AcidsReactions of Carboxylic Acids
DecarboxylationDecarboxylation
But first we revisit acid-catalyzed esterificationBut first we revisit acid-catalyzed esterificationto examine its mechanism.to examine its mechanism.
New reaction in this chapterNew reaction in this chapter
Dr. Wolf's CHM 201 & 202 18-59
Mechanism of Acid-Catalyzed Esterification
Dr. Wolf's CHM 201 & 202 18-60
Acid-catalyzed EsterificationAcid-catalyzed Esterification
++ CHCH33OOHH
COHCOH
OOHH++
++ HH22OO
CCOOCHCH33
OO
Important fact: the Important fact: the oxygenoxygen of the alcohol is of the alcohol isincorporated into the ester as shown.incorporated into the ester as shown.
(also called Fischer esterification)(also called Fischer esterification)
Dr. Wolf's CHM 201 & 202 18-61
The mechanism involves two stages: The mechanism involves two stages:
1)1) formation of tetrahedral intermediateformation of tetrahedral intermediate(3 steps)(3 steps)
2)2) dissociation of tetrahedral intermediate dissociation of tetrahedral intermediate (3 steps)(3 steps)
Mechanism of Fischer Esterification
Mechanism of Fischer Esterification
Dr. Wolf's CHM 201 & 202 18-62
The mechanism involves two stages: The mechanism involves two stages:
1)1) formation of tetrahedral intermediateformation of tetrahedral intermediate(3 steps)(3 steps)
2)2) dissociation of tetrahedral intermediate dissociation of tetrahedral intermediate (3 steps)(3 steps)
Mechanism of Fischer Esterification
Mechanism of Fischer Esterification
CC
OHOH
OHOH
OOCHCH33
tetrahedral intermediate in esterification tetrahedral intermediate in esterification of benzoic acid with methanolof benzoic acid with methanol
Dr. Wolf's CHM 201 & 202 18-63
First stage: formation of tetrahedral intermediate
First stage: formation of tetrahedral intermediate
CC
OHOH
OHOH
OOCHCH33
++ CHCH33OOHH
COHCOH
OO
HH++
methanol adds to the methanol adds to the carbonyl group of the carbonyl group of the carboxylic acidcarboxylic acid
the tetrahedral the tetrahedral intermediate is intermediate is analogous to a analogous to a hemiacetalhemiacetal
Dr. Wolf's CHM 201 & 202 18-64
Second stage: conversion of tetrahedral intermediate to esterSecond stage: conversion of
tetrahedral intermediate to ester
CC
OHOH
OHOH
OOCHCH33
++ HH22OO
HH++this stage corresponds this stage corresponds to an acid-catalyzed to an acid-catalyzed dehydrationdehydration
CCOOCHCH33
OO
Dr. Wolf's CHM 201 & 202 18-65
Mechanism of formationof
tetrahedral intermediate
Mechanism of formationof
tetrahedral intermediate
Dr. Wolf's CHM 201 & 202 18-66
Step 1Step 1 CC
OO
OO HH
•••• ••••
••••••••
OO ••••++HH
CHCH33
HH
Dr. Wolf's CHM 201 & 202 18-67
Step 1Step 1 CC
OO
OO HH
•••• ••••
••••••••
OO ••••++HH
CHCH33
HH
••••
CC
OO
OO HH
••••
••••
++ HH •••• OO ••••
CHCH33
HH
Dr. Wolf's CHM 201 & 202 18-68
Step 1Step 1
••••
CC
OO
OO HH
••••
••••
++ HH
carbonyl oxygen is carbonyl oxygen is protonated because protonated because cation produced is cation produced is stabilized by electron stabilized by electron delocalization delocalization (resonance)(resonance)
CC
OO
OO HH
••••••••
++
HH
••••
Dr. Wolf's CHM 201 & 202 18-69
Step 2Step 2
••••
CC
OO
OO HH
••••
••••
++ HH
•••• OO ••••
CHCH33
HH
Dr. Wolf's CHM 201 & 202 18-70
Step 2Step 2
••••
CC
OO
OO HH
••••
••••
++ HH
•••• OO ••••
CHCH33
HH
CC
OHOH
OHOH
••••••••
••••••••
OO ••••++
CHCH33
HH
Dr. Wolf's CHM 201 & 202 18-71
Step 3Step 3
•••• OO ••••
CHCH33
HH••••
CC
OHOH
OHOH
••••••••
••••
OO ••••
CHCH33
HH
++
Dr. Wolf's CHM 201 & 202 18-72
Step 3Step 3
•••• OO ••••
CHCH33
HH
••••
CC
OHOH
OHOH
••••••••
••••
OO ••••
CHCH33
HH
++ OO ••••
CHCH33
HH
HH++
••••
CC
OHOH
OHOH
••••••••
••••
OO ••••
CHCH33
••••
Dr. Wolf's CHM 201 & 202 18-73
Tetrahedral intermediateto
ester stage
Tetrahedral intermediateto
ester stage
Dr. Wolf's CHM 201 & 202 18-74
Step 4Step 4
••••
CC
OHOH
OO
••••••••
••••
OOCHCH33••••
••••
HH
Dr. Wolf's CHM 201 & 202 18-75
Step 4Step 4
OO ••••
CHCH33
HH
HH++••••
CC
OHOH
OO
••••••••
••••
OOCHCH33••••
••••
HH
Dr. Wolf's CHM 201 & 202 18-76
Step 4Step 4
OO ••••
CHCH33
HH
HH++••••
CC
OHOH
OO
••••••••
••••
OOCHCH33••••
••••
HH
••••
CC
OHOH
OO
••••••••
OOCHCH33••••
••••
HH HH++ •••• OO ••••
CHCH33
HH
Dr. Wolf's CHM 201 & 202 18-77
Step 5Step 5
••••
CC
OHOH
OO
••••••••
OOCHCH33••••
••••
HH HH++
Dr. Wolf's CHM 201 & 202 18-78
Step 5Step 5
••••
CC
OHOH
OO
••••••••
OOCHCH33••••
••••
HH HH++
OO••••HH HH••••
++
CC
OHOH••••••••
OOCHCH33••••
••••
++
Dr. Wolf's CHM 201 & 202 18-79
Step 5Step 5
CC
OHOH••••••••
OOCHCH33••••
••••
++
CC
OHOH••••
OOCHCH33••••
••••
++
Dr. Wolf's CHM 201 & 202 18-80
Step 6Step 6
CC
OO••••
OOCHCH33••••
••••
++ HH
OO••••
HH CHCH33•••• ++OOHH CHCH33••••
HH CC
OO••••
OOCHCH33••••
••••
••••
Dr. Wolf's CHM 201 & 202 18-81
Activation of carbonyl group by protonation of Activation of carbonyl group by protonation of carbonyl oxygencarbonyl oxygen
Nucleophilic addition of alcohol to carbonyl groupNucleophilic addition of alcohol to carbonyl groupforms tetrahedral intermediateforms tetrahedral intermediate
Elimination of water from tetrahedral intermediate Elimination of water from tetrahedral intermediate restores carbonyl grouprestores carbonyl group
Key Features of MechanismKey Features of Mechanism
Dr. Wolf's CHM 201 & 202 18-82
Intramolecular Ester Formation:Lactones
Dr. Wolf's CHM 201 & 202 18-83
Lactones are cyclic estersLactones are cyclic esters
Formed by intramolecular esterification in aFormed by intramolecular esterification in acompound that contains a hydroxyl group andcompound that contains a hydroxyl group anda carboxylic acid functiona carboxylic acid function
LactonesLactones
Dr. Wolf's CHM 201 & 202 18-84
ExamplesExamples
HHOOCHCH22CHCH22CHCH22COHCOH
OO OO
OO++ HH22OO
4-hydroxybutanoic acid4-hydroxybutanoic acid 4-butanolide4-butanolide
IUPAC nomenclature: replace the IUPAC nomenclature: replace the -oic acid -oic acid ending of the carboxylic acid by ending of the carboxylic acid by -olide-olide
identify the oxygenated carbon by numberidentify the oxygenated carbon by number
Dr. Wolf's CHM 201 & 202 18-85
ExamplesExamples
HHOOCHCH22CHCH22CHCH22COHCOH
OO
HHOOCHCH22CHCH22CHCH22CHCH22COHCOH
OO OO
OO
OO
OO++
++
HH22OO
HH22OO
4-hydroxybutanoic acid4-hydroxybutanoic acid
5-hydroxypentanoic acid5-hydroxypentanoic acid
4-butanolide4-butanolide
5-pentanolide5-pentanolide
Dr. Wolf's CHM 201 & 202 18-86
Common namesCommon names
OOOO
OO
OO
-butyrolactone-butyrolactone -valerolactone-valerolactone
Ring size is designated by Greek letter Ring size is designated by Greek letter corresponding to oxygenated carboncorresponding to oxygenated carbon
A A lactone has a five-membered ring lactone has a five-membered ring
A A lactone has a six-membered ring lactone has a six-membered ring
Dr. Wolf's CHM 201 & 202 18-87
Reactions designed to give hydroxy acids often Reactions designed to give hydroxy acids often yield the corresponding lactone, especially if theyield the corresponding lactone, especially if theresulting ring is 5- or 6-membered.resulting ring is 5- or 6-membered.
LactonesLactones
Dr. Wolf's CHM 201 & 202 18-88
ExampleExample
5-hexanolide (78%)5-hexanolide (78%)
OO
HH33CC
OO
CHCH33CCHCCH22CHCH22CHCH22COHCOH
OOOO
1. NaBH1. NaBH44
2. H2. H22O, HO, H++
Dr. Wolf's CHM 201 & 202 18-89
ExampleExample
5-hexanolide (78%)5-hexanolide (78%)
via:via: OO
HH33CC
OO
CHCH33CCHCCH22CHCH22CHCH22COHCOH
OOOO
1. NaBH1. NaBH44
2. H2. H22O, HO, H++
CHCH33CHCHCHCH22CHCH22CHCH22COHCOH
OOOOHH
Dr. Wolf's CHM 201 & 202 18-90
Decarboxylation of Malonic Acid
and Related Compounds
Dr. Wolf's CHM 201 & 202 18-91
Decarboxylation of Carboxylic Acids
Decarboxylation of Carboxylic Acids
Simple carboxylic acids do not decarboxylateSimple carboxylic acids do not decarboxylatereadily.readily.
RHRH ++ COCO22RCOHRCOH
OO
Dr. Wolf's CHM 201 & 202 18-92
Decarboxylation of Carboxylic Acids
Decarboxylation of Carboxylic Acids
Simple carboxylic acids do not decarboxylateSimple carboxylic acids do not decarboxylatereadily.readily.
But malonic acid does.But malonic acid does.
RHRH ++ COCO22RCOHRCOH
OO
150°C150°CCHCH33COHCOH
OO
++ COCO22HOCCHHOCCH22COHCOH
OO OO
Dr. Wolf's CHM 201 & 202 18-93
Mechanism of DecarboxylationMechanism of Decarboxylation
One carboxyl group assists the loss of the other.One carboxyl group assists the loss of the other. OO OO
OHOHHOHO
HH HH
OO
HOHO OO
OO
HH HH
HH
Dr. Wolf's CHM 201 & 202 18-94
Mechanism of DecarboxylationMechanism of Decarboxylation
This compound is This compound is the enol form of the enol form of acetic acid.acetic acid.
OO OO
OHOHHOHO
HH HH HH
HH
OHOH
HOHO
OO
HOHO OO
OO
HH HH
HH ++ CC
OO
OO
One carboxyl group assists the loss of the other.One carboxyl group assists the loss of the other.
Dr. Wolf's CHM 201 & 202 18-95
Mechanism of DecarboxylationMechanism of Decarboxylation OO OO
OHOHHOHO
HH HH HH
HH
OHOH
HOHO
OO
HOHO OO
OO
HH HH
HH ++ CC
OO
OO
One carboxyl group assists the loss of the other.One carboxyl group assists the loss of the other.
HOCCHHOCCH33
OO
Dr. Wolf's CHM 201 & 202 18-96
Mechanism of DecarboxylationMechanism of Decarboxylation OO OO
OHOHHOHO
HH HH HH
HH
OHOH
HOHO
OO
HOHO OO
OO
HH HH
HH ++ CC
OO
OO
One carboxyl group assists the loss of the other.One carboxyl group assists the loss of the other.
HOCCHHOCCH33
OO
These hydrogens play no role.These hydrogens play no role.
Dr. Wolf's CHM 201 & 202 18-97
Mechanism of DecarboxylationMechanism of Decarboxylation OO OO
OHOHHOHO
RR R'R' RR
R'R'
OHOH
HOHO
OO
HOHO OO
OO
RR R'R'
HH ++ CC
OO
OO
One carboxyl group assists the loss of the other.One carboxyl group assists the loss of the other.
HOCCHHOCCHR'R'
OO
Groups other than H may be present.Groups other than H may be present.
RR
Dr. Wolf's CHM 201 & 202 18-98
185°C185°C
Decarboxylation is a general reaction for 1,3-dicarboxylic acids
Decarboxylation is a general reaction for 1,3-dicarboxylic acids
160°C160°C
COCO22HH
COCO22HH
COCO22HH
HH
(74%)(74%)
(96-99%)(96-99%)
CH(COCH(CO22H)H)22
CHCH22COCO22HH
Dr. Wolf's CHM 201 & 202 18-99
Mechanism of DecarboxylationMechanism of Decarboxylation OO OO
OHOHHOHO
RR R'R' RR
R'R'
OHOH
HOHO
OO
HOHO OO
OO
RR R'R'
HH ++ CC
OO
OO
One carboxyl group assists the loss of the other.One carboxyl group assists the loss of the other.
This OH group plays no role.This OH group plays no role.
HOCCHHOCCHR'R'
OO
RR
Dr. Wolf's CHM 201 & 202 18-100
Mechanism of DecarboxylationMechanism of Decarboxylation OO OO
OHOHR"R"
RR R'R'
RR
CC
OO
OO
One carboxyl group assists the loss of the other.One carboxyl group assists the loss of the other.
Groups other than OH may be present.Groups other than OH may be present.
R"R"CCHCCHR'R'
OO
RR
OO
OO
OO
RR R'R'
HH R"R"
R'R'
OHOH
++R"R"
Dr. Wolf's CHM 201 & 202 18-101
Mechanism of DecarboxylationMechanism of Decarboxylation OO OO
OHOHR"R"
RR R'R'
This kind of compoundThis kind of compoundis called a is called a -keto acid.-keto acid.
R"R"CCHCCHR'R'
OO
RR
Decarboxylation of a Decarboxylation of a -keto acid gives a -keto acid gives a ketone.ketone.
Dr. Wolf's CHM 201 & 202 18-102
Decarboxylation of a -Keto AcidDecarboxylation of a -Keto Acid
CCCHCH33CC
OO
CHCH33
CHCH33
COCO22HH25°C25°C
COCO22
CCCHCH33CC
OO
CHCH33
CHCH33
HH
++
Dr. Wolf's CHM 201 & 202 18-103
Spectroscopic Analysis ofSpectroscopic Analysis ofCarboxylic AcidsCarboxylic Acids
Dr. Wolf's CHM 201 & 202 18-104
A carboxylic acid is characterized by peaks due toA carboxylic acid is characterized by peaks due toOH and C=O groups in its infrared spectrum.OH and C=O groups in its infrared spectrum.
C=O stretching gives an intense absorptionC=O stretching gives an intense absorptionnear 1700 cmnear 1700 cm-1-1..
OH peak is broad and overlaps with C—H OH peak is broad and overlaps with C—H absorptions.absorptions.
Infrared SpectroscopyInfrared SpectroscopyInfrared SpectroscopyInfrared Spectroscopy
Dr. Wolf's CHM 201 & 202 18-105
2000200035003500 30003000 25002500 1000100015001500 500500
Wave number, cmWave number, cm-1-1
Figure 19.8 Infrared Spectrum of 4-Phenylbutanoic acidFigure 19.8 Infrared Spectrum of 4-Phenylbutanoic acidFigure 19.8 Infrared Spectrum of 4-Phenylbutanoic acidFigure 19.8 Infrared Spectrum of 4-Phenylbutanoic acid
C=OC=O
O—H and C—H stretchO—H and C—H stretch
monosubstitutedmonosubstitutedbenzenebenzene
CC66HH55CHCH22CHCH22CHCH22COCO22HH
Dr. Wolf's CHM 201 & 202 18-106
proton of OH group of a carboxylic acid is normallyproton of OH group of a carboxylic acid is normallythe least shielded of all of the protons in a the least shielded of all of the protons in a 11HHNMR spectrum: (NMR spectrum: ( 10-12 ppm; broad). 10-12 ppm; broad).
11H NMRH NMR11H NMRH NMR
Dr. Wolf's CHM 201 & 202 18-107
Chemical shift (Chemical shift (, ppm), ppm)
Figure 19.9Figure 19.9
CCHH22CCHH22CCHH22COCOHH
OO
01.02.03.04.05.06.07.08.09.010.011.012.0
Dr. Wolf's CHM 201 & 202 18-108
1313C NMRC NMR1313C NMRC NMR
Carbonyl carbon is at low field (Carbonyl carbon is at low field ( 160-185 ppm), 160-185 ppm), but not as deshielded as the carbonyl carbon of but not as deshielded as the carbonyl carbon of an aldehyde or ketone (an aldehyde or ketone ( 190-215 ppm). 190-215 ppm).
Dr. Wolf's CHM 201 & 202 18-109
UV-VISUV-VISUV-VISUV-VIS
Carboxylic acids absorb near 210 nm, butCarboxylic acids absorb near 210 nm, butUV-VIS spectroscopy has not proven to UV-VIS spectroscopy has not proven to be very useful for structure determination of be very useful for structure determination of carboxylic acids.carboxylic acids.
Dr. Wolf's CHM 201 & 202 18-110
Aliphatic carboxylic acids undergo a varietyAliphatic carboxylic acids undergo a varietyof fragmentations.of fragmentations.Aromatic carboxylic acids first form acylium ions,Aromatic carboxylic acids first form acylium ions,which then lose CO.which then lose CO.
Mass SpectrometryMass SpectrometryMass SpectrometryMass Spectrometry
ArCArCOHOH
••••OO ••
••
ArCArCOHOH
••++OO ••
••
ArCArC OO ••••
++ArAr+
+
Dr. Wolf's CHM 201 & 202 18-111
End of Chapter 18